The appearance of new equipment on board airplanes, such as IFE (In Flight Entertainment) systems allowing, for example, distribution of on-demand video to passengers, has led to a constant increase in cabling in the passenger cabins of airplanes. This not only poses weight problems, but also installation and maintenance cost problems, in addition to problems of configurability of the passenger cabin.
Solutions using wireless communication technologies via radiowaves, such as connections conforming to the standard IEEE802.11, better known by the commercial name “wi-fi connection”, are currently in the process of being researched and tested. Other solutions using wireless communication technologies via light waves, such as the IrDA protocol, the acronym meaning “Infrared Data Association”, are also in the process of being researched and tested. Unfortunately, for diverse reasons, these current solutions have only led to a moderately significant reduction in the quantity of cabling. This is because a line of cables, better known by the name “backbone”, still passes longitudinally through the passenger cabin for carrying the signals from the server to the immediate proximity of the seats. Only the last part is realized by a wireless wi-fi or IrDA connection. Often the backbone is situated in the ceiling of the passenger cabin. It should be noted, however, that these solutions based on wi-fi or IrDA technology partly solve the problem of configurability of the passenger cabin for which they were designed. Indeed, the first IFE systems, which used a wired connection through to the seats, meant that the arrangement of the seats could hardly be adjusted. This is no longer the case with solutions combining a wired backbone with a wi-fi connection or combining a wired backbone with an IrDA connection, as the seat is no longer connected by a wire to the IFE system. But these solutions only ease the problem of weight and of additional cost linked with the use of cables: it is still necessary to have a cabled backbone in the ceiling of the passenger cabin. And in addition they do not solve the possible problems of electromagnetic interference in the wi-fi band.
The present invention proposes notably replacing the cabled backbone with a wireless backbone, this being done by exploiting free-air infrared laser beam communication technology. This is because an infrared laser beam is capable of carrying information at high speed without data compression, whether this is on an optical medium such as glass fiber or simply by allowing the light beam to propagate freely in the air. For example, this technology is a practical and economical solution for establishing a point-to-point connection covering the “last mile” in long-haul networks. But it is also used from the roof of buildings in urban local networks. This technology has the decisive advantage that, in contrast to radio communications, the use of an optical laser is not subject to any license being obtained. It also has great flexibility of use in terms of installation and deinstallation: it does not require any heavy infrastructure requiring civil engineering works. But implementing such a technology on board an airplane is not without many difficulties.
This poses, among others, a problem of sighting. Indeed, it is imperative to establish and to maintain precise alignment between the elements of the connection so that the beam connects these elements properly to each other. The mechanical constraints to which an airplane is subjected, notably the deformations and vibrations, make it difficult to maintain such a sighting. The connection is therefore frequently interrupted, occasioning significant information losses which even high-performance communication protocols fail to correct.
Moreover, the use of a laser beam in a busy environment such as the passenger cabin of an airplane is not without danger. For even a low-power laser might represent a real danger to the eye by causing irreparable burns to the retina. This is furthermore why devices diffusing a laser beam are classed in six standard classes, which are Class I, Class II, Class IIa, Class IIIa, Class IIIb and Class IV lasers, each category notably representing a hazard level for the eyesight.
In addition, the problem for an IFE system, consisting in a server sending data to several clients, does not seem really to correspond to the problem for current point-to-point systems using laser transmission to send data from a server to a single client.